/Engine/Source/Runtime/UMG/Public/Binding/States/WidgetStateRegistration.h
Technically these can be created in BP, but for now we don't want to encourage that workflow as it involves requring overrides for the virtuals which is technical.
class UWidgetBinaryStateRegistration : public [UObject](API\Runtime\CoreUObject\UObject\UObject)
friend
UWidgetStateSettings